|MadSci Network: General Biology|
The most common sugar measurement used for fruit is soluble sugar, or the amount of sugar in juice of the apple. This method only requires a small amount of juice and is very fast. The tool used to measure soluble sugar is a refractometer. The following comes from the catalog of the Cole-Parmer Instrument Company How a refractometer works: When light enters a liquid it changes direction; this is called refraction. Refractometers measure the degree to which the light changes direction, called the angle of refraction. A refractometer takes the refraction angles and correlates them to the refractive index (nD) values that have been established. Using these values, you can determine the concentrations of solutions. For example, solutions have different refractive indexes depending on their concentration in water. The prism in the refractometer has a greater refractive index than the solution. Measurements are read at the point where the prism and solution meet. With a low concentration in solution, the refractive index of the prism is much greater than that of the sample, creating a large refraction angle and a low reading. The reverse would happen with a high concentrated solution. Sugar is measured in Brix, which is a scale calibrated to the number of grams of cane sugar contained in 100 ml of water. Therefore, the Brix % reading equals actual sugar concentration. In an apple the Brix is typically 11 to 18 percent. As you can see, the principle is fairly simple. I hope this helps. Eric Biddinger Graduate student Department of Horticulture Penn State University
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